The present invention relates to optical lenses and more particularly to miniature lenses having a wide-angle field of view.
For most applications requiring wide-angle imaging, larger lens constructions having a miniaturization ratio (i.e., a total track length over an image circle diameter) greater than 3.0 are often used. However, for consumer applications, especially with mobile devices, the trend is that the lens thicknesses are becoming thinner while the sensor sizes are becoming larger. Accordingly, a new kind of wide-angle lenses with a miniaturization ratio less than 3.0 are required.
Previously suggested miniature wide-angle lenses, such as that described in “Consumer electronic optics: how small can a lens be: the case of panomorph lenses” published in “Proc. SPIE 9192, Current Developments in Lens Design and Optical Engineering XV, 91920H,” or as in U.S. Pat. No. 8,248,715 or U.S. Pat. App. Pub. Nos. 2014/0029115, 2013/0308206, 2014/0226222, 2014/0285906, 2015/0253542, 2015/0268446 or 2012/0212839 were designed for previous generations of sensors having smaller sizes and larger pixels. These lenses had lower performance requirements, especially regarding image quality and aperture size. For these existing lens constructions, a total of three to six optical elements were enough to meet the required performances for these sensors. For the existing wide-angle 6-element lenses, a symmetric construction using 3 elements in front of the stop and 3 elements behind the stop has been used. However, with new larger sensors and smaller pixels, more complex wide-angle lens constructions using six elements with asymmetric constructions around the stop or using seven or more elements must be designed to achieve the required performances.
One of the challenges to achieve good imaging performance over the whole field of view of a miniature wide-angle lens is the change of relative illumination from the center to the edge of the field of view. In wide-angle lenses, the relative illumination is usually maximum in the center and drops continuously toward the edge of the field of view. The consequence of lower illumination toward the edge is a lower image quality at the edge due to increased diffraction effects and additional sensor noise at the edges.
Another challenge to achieve good imaging performance over the whole field of view of a miniature wide-angle lens is a drop of the modulation transfer function (MTF) from the center to the edge of the field of view. In wide-angle lenses, the image MTF is usually maximum in the center and drops continuously toward the edge of the field of view. The consequence of lower MTF toward the edge is a lower image quality at the edge.